Medical imaging is a field dominated by high cost systems that may be so complex as to require specialized technicians for operation and the services of experienced medical doctors and nurses for image interpretation. Medical ultrasound, which is considered a low cost modality, utilizes imaging systems costing as much as $250K, or more. These systems may be operated by technicians with two years of training or specialized physicians. This high-tech, high-cost approach works very well for critical diagnostic procedures. However it makes ultrasound impractical for many of the routine tasks for which it would be clinically useful.
A number of companies have attempted to develop low cost, easy to use systems for more routine use. One example of such an attempt is that by Sonosite. The Sonosite system produces very high quality images at a system cost of at least $20,000. While far less expensive than high-end systems, these systems are still very sophisticated and require a well-trained operator. Furthermore, at this price few new applications may be opened.
Many ultrasonic imaging systems utilize an array transducer that is connected to beamformer circuitry through a cable, and a display that is usually connected directly to or integrated with the beamformer. This approach is attractive because it allows the beamformer electronics to be as large as is needed to produce an economical system. In addition, the display may be of a very high quality.
Some conventional system architectures have been improved upon through reductions in beamformer size. One of the most notable efforts has been undertaken by Advanced Technologies Laboratories and then continued by a spin-off company, Sonosite. U.S. Pat. No. 6,135,961 to Pflugrath et al., entitled “Ultrasonic Signal Processor for a Hand Held Ultrasonic Diagnostic Instrument,” hereby incorporated by reference herein in its entirety, describes some of the signal processing employed to produce a highly portable ultrasonic imaging system. The Pflugrath '961 patent makes reference to an earlier U.S. Pat. No. 5,817,024 to Ogle et al., entitled, “Hand Held Ultrasonic Diagnostic instrument with Digital Beamformer,” hereby incorporated by reference herein in its entirety. In U.S. Pat. No. 6,203,498 to Bunce et al., entitled “Ultrasonic Imaging Device with Integral Display,” hereby incorporated by reference herein in its entirety, however, the transducer, beamformer, and display may be all integrated to produce a very small and convenient imaging system.
Other references of peripheral interest are U.S. Pat. No. 6,669,641 to Poland, et al., entitled “Method of and system for ultrasound imaging,” which is hereby incorporated herein, in its entirety, by reference thereto, which describes an ultrasonic apparatus and method in which a volumetric region of the body is imaged by biplane images. One biplane image has a fixed planar orientation to the transducer, and the plane of the other biplane image can be varied in relation to the fixed reference image.
U.S. Pat. No. 6,491,634 to Leavitt, et al., entitled “Sub-beam-forming apparatus and method for a portable ultrasound imaging,” which is hereby incorporated herein, in its entirety, by reference thereto, describes a sub-beam-forming method and apparatus that is applied to a portable, one-dimensional ultrasonic imaging system. The sub-beam-forming circuitry may be included in the probes assembly housing the ultrasonic transducer, thus minimizing the number of signals that are communicated between the probe assembly and the portable processor included in the imaging system.
U.S. Pat. No. 6,380,766 to Savord, entitled “Integrated circuitry for use with transducer elements in an imaging system,” which is hereby incorporated herein, in its entirety, by reference thereto, describes integrated circuitry for use with an ultrasound transducer of an ultrasound imaging system.
U.S. Pat. No. 6,013,032 to Savord, entitled “Beam-forming methods and apparatus for three-dimensional ultrasound imaging using two-dimensional transducer array,” which is hereby incorporated herein, in its entirety, by reference thereto, describes an ultrasound imaging system including a two-dimensional array of ultrasound transducer elements that define multiple sub-arrays, a transmitter for transmitting ultrasound energy into a region of interest with transmit elements of the array, a sub-array processor and a phase shift network associated with each of the sub-arrays, a primary beam-former and an image generating circuit.
U.S. Pat. No. 6,126,602 to Savord, et al., entitled “Phased array acoustic systems with intra-group processors,” which is hereby incorporated herein, in its entirety, by reference thereto, describes an ultrasound imaging apparatus and method that uses a transducer array with a very large number of transducer elements or a transducer array with many more transducer elements than beam-former channels.
U.S. Pat. No. 5,997,479 to Savord, et al., entitled “Phased array acoustic systems with intra-group processors,” which is hereby incorporated herein, in its entirety, by reference thereto, describes an ultrasound imaging apparatus and method that uses a transducer array with a very large number of transducer elements or a transducer array with many more transducer elements than beam-former channels.
U.S. Pat. No. 6,582,372 to Poland, entitled “Ultrasound system for the production of 3-D images,” which is hereby incorporated herein, in its entirety, by reference thereto, describes an ultrasound system that utilizes a probe in conjunction with little or no specialized 3-D software/hardware to produce images having depth cues.
U.S. Pat. No. 6,179,780 to Hossack, et al., entitled “Method and apparatus for medical diagnostic ultrasound real-time 3-D transmitting and imaging,” which is hereby incorporated herein, in its entirety, by reference thereto, describes a medical diagnostic ultrasound real-time 3-D transmitting and imaging system that generates multiple transmit beam sets using a 2-D transducer array.
U.S. Pat. No. 6,641,534 to Smith, et al., entitled “Methods and devices for ultrasound scanning by moving sub-apertures of cylindrical ultrasound transducer arrays in two dimensions,” which is hereby incorporated herein, in its entirety, by reference thereto, describes methods of scanning using a two dimensional (2-D) ultrasound transducer array.
U.S. Pat. No. 4,949,310 to Smith, et al., entitled “Maltese cross processor: a high speed compound acoustic imaging system,” which is hereby incorporated herein, in its entirety, by reference thereto, describes an electronic signal processing device which forms a compound image for any pulse-echo ultrasound imaging system using a two-dimensional array transducer.
U.S. Pat. No. 6,276,211 to Smith, entitled “Methods and systems for selective processing of transmit ultrasound beams to display views of selected slices of a volume,” which is hereby incorporated herein, in its entirety, by reference thereto, describes the selection of a configuration of slices of a volume, such as B slices, I slices, and/or C slices.
U.S. Patent Application Publication No. US 2010/0312106 to Blalock et al., entitled “Ultrasound Imaging Beam-Former Apparatus and Method, which is hereby incorporated herein, in its entirety, by reference thereto, describes an ultrasound imaging beamformer apparatus in which an incoming signal from a transducer is applied to an in-phase sample-and-hold and a quadrature sample-and-hold.
U.S. Patent Application Publication No. US 2010/0063399 to Walker et al., entitled “Front End Circuitry for Imaging Systems and Methods of Use,” which is hereby incorporated herein, in its entirety, by reference thereto, describes front end circuitry including a receive circuit configured to receive signals generated using coded excitation, perform analog sampling the received electrical signals generated using coded excitation, and provide a weighted, summed digital signal by processing the analog samples.
U.S. Patent Application Publication No. US 2007/0016044 to Blalock et al., entitled “Ultrasonic Transducer Drive,” which is hereby incorporated herein, in its entirety, by reference thereto, describes a shunt that is connectable between a receive side of an ultrasonic transducer and a reference potential. A signal generator may generate an outgoing signal during a period of time while the shunt connects the receive side of the transducer to the reference potential. A signal receiver may receive an incoming signal during a period while the shunt is substantially open.
U.S. Patent Application Publication No. US 2007/0016022 to Blalock et al., entitled “Ultrasonic Imaging Beam-Former Apparatus and Method,” which is hereby incorporated herein, in its entirety, by reference thereto, describes an incoming signal from a transducer in an ultrasound imaging beam-formed apparatus that is applied to an in-phase sample-and-hold and a quadrature sample-and-hold.
A schematic diagram of a transducer drive 10 for a conventional phased array ultrasound system is shown in FIG. 1. A piezoelectric transducer array 12, shown on the left, acts as an interface to a signal processor by converting electrical signals to acoustic pulses and vice versa. Images may be formed by transmitting a series of acoustic pulses from the transducer array 12 and displaying signals representative of the magnitude of the echoes received from these pulses. Low voltage receive electronics 14 receive electrical signals form the transducer and process the signals to form images. A relatively high voltage transmit generator generates a relatively high-voltage electrical signals that are inputted to the transducer array 12 to be transduced to outgoing ultrasound. Transmit/Receive (T/R) high voltage switches 18 are provided that are switchable from one configuration, in which switches 18 electrically connect the transmit generator 16 to the transducer array 12 to input relatively high voltage electrical signals to the transducer array, to a second configuration, in which switches 18 electrically connect the transducer array 12 to the low-voltage receive electronics 14.
Image formation begins when T/R switches are placed in the first configuration to connect the transducer elements 12 to individual transmit circuits. Next, transmit generators 16 output time varying waveforms with delay and amplitude variations selected to produce a desired acoustic beam. Voltages of up to 200 Volts or more may be applied to the transducer elements 12. Once transmission is complete, the T/R high voltage switches 18 are switched to the second configuration to connect the transducer elements 12 to individual receive circuitry (in the low voltage receive electronics 14) associated with each element.
Note that the transducer array 12 shown in FIG. 1 has one common electrode 13, and the non-common electrodes may be multiplexed between high-voltage transmit and low-voltage receive signals. The conventional T/R high voltage switches 18 are the source of considerable expense and bulk in typical ultrasound systems. For modern, three-dimensional (3D) ultrasound systems, the channel count (and thus, the number of T/R high voltage switches required) can reach into the thousands making the bulk and expense of the high voltage switches impractical, if not prohibitive.
Ultrasonic transducers associated with ultrasound imaging systems may be driven from a single terminal with the second terminal grounded. A transducer may be used to transmit ultrasound signals as well as receive reflected ultrasound.
A signal received at a transducer (reflected signal) may typically be several orders of magnitude smaller than the signal (outgoing signal) that was transmitted due to, inter alia, signal attenuation by the target tissue. Some of the signal may be lost due to transducer inefficiencies as well. It may be thus necessary to couple the transducer to a high-voltage transmit signal while the ultrasound is being transmitted, and then to a sensitive low-noise preamplifier while the reflected ultrasound is being received.
A switch that couples the transducer to the transmit and receive signals must be capable of withstanding high peak transmit voltages (typically 50-200 volts) while isolating the preamplifier input from those voltage levels, since they would otherwise destroy the preamplifier. If a receiver for the signals from the transducers is fabricated as a high-density, low-voltage integrated circuit (IC), the switches themselves may need to be fabricated off-chip in a separate package from materials and devices that can withstand the high voltage transmit pulses.
Commercial ultrasound systems have been limited to one-dimensional (1-D) or linear transducer arrays until fairly recently. A typical number of transducers in such an array may be 128. Providing separate multiplex and receive circuitry is manageable with this many transducers, albeit with significant use of expensive high-voltage switches. Newer arrays, however, may be likely to be two-dimensional (2-D) or square arrays. The number of transducers in a two-dimensional array may range up to 128×128 or 16,384, and is often in the thousands. Maintaining separate receive, transmit, and multiplex partitioning for the transducers in such an array creates a tremendous burden in terms of cost, space, and complexity. The power consumption and heat dissipation of thousands of high-voltage multiplexers is enough to discourage the use of two-dimensional arrays in portable ultrasound imaging systems.
Accordingly, existing ultrasound systems with thousands of separate transmit and receive switches may be too expensive and/or too bulky for many applications. While a variety of systems and methods may be known, there remains a need for improved systems and methods.